The present invention relates to processes, means and devices using electromagnetic radiation for the determination of a component of a group of specifically bonding receptors and substances which can be specifically bonded by these receptors, in particular to processes, means and devices for the immunological determination of antibodies, antigens and haptens.
The most usual processes for sensitive immunological determination of antibodies, antigens and haptens are based on the use of labelling substances, such as radioisotopes, enzymes or fluorochromes, which are coupled chemically to one of the components. The necessity of coupling antibodies, antigens or haptens to such a labelling substance has, however, a number of substantial disadvantages: chemical linking of an antibody (antigen) to, for example, an enzyme produces interference in the bonding properties of the antibody (antigen), i.e., its bonding affinity decreases; chemical linking of an enzyme to an antibody (antigen) leads to a substantial reduction in the enzymatic activity; the stability of the conjugates is lower than the stability of the individual substances; the conjugates are very heterogeneous compounds with a broad molecular weight spectrum, so that reproducible preparation is made extremely difficult; and for bonding of conjugates to a solid phase, the enzymatic activity is affected by diffusion of substrates and products.
Because of such disadvantages, there is a need for simpler methods, for example enabling direct measurement of the immunological reaction. Such processes are already known, but are either not sensitive enough, as in the case of turbidity measurements, or too expensive and too complicated, as in the case of determination of antigen-antibody layers on metal surfaces by ellipsometry.
A measurement arrangement for the determination of thin layers, which is somewhat simplified in comparison with a conventional ellipsometer, is described in European Patent Application 19,088, wherein essentially only the compensator of an ellipsometer is replaced by a reference surface. German Offenlegungsschrift 2,638,250 describes a simple process for measuring antigen-antibody layers on glasses coated with metal beads. This certainly by-passes the difficulties of ellipsometry, but only provides semi-quantitative information.